Switch



April 1, 1947. v H. E. WHlTE ,3

SWITCH Filed Feb. 25, 1944 INVEN TOR.

ITTORNFY Patented Apr. 1, 1947 UNITED STATES PATENT OFFICE 3 Claims.

My invention pertains to thermostatic switches.

An object of my invention is to provide a new and improved thermostaticswitch.

Another object of my invention is to provide a lei-metallic type ofthermostatic switch which is sensitive to small changes in temperature.

It is another object of my invention to provide a thermostatic switchwhich responds rapidly to changes in temperature.

A further object of my invention is to provide a small circularly shapedthermostatic switch.

It is also an object of my invention to provide a thermostatic switchhaving a plurality of adjustment means for determining the temperaturerange over which it operates.

An object of my invention is to provide a ther mostatic switch for usein a low voltage circuit, and one which may stand unused for longperiods 01"" time in a dusty place and still operate.

A. detailed object of my invention is to provide a new and improvedthermostatic switch for operating a fire alarm from a low-voltageelectrical circuit such as a door bell ircuit, and which may remainunused for years in a dusty place and still operate eificiently in spiteof a dirt film, should the emergency arise.

Other objects and a fuller understanding of my invention maybe had byreferring to the following description and claims, read in conjunctionwith the drawings in which:

Figure 1 is a side view of my thermostatic switch.

Figure 2 is a top view of the switch shown in Figure 1.

Figure 3 is a sectional view taken along lines 3--3 of Figure 2.

Figure 4 is a sectional view taken along lines 4-4 of Figure 1, showingthe contacts in their open position.

Figure 5 is a sectional view similar to Figure 4, but showing thecontacts in their closed position.

Figure 6 is a view of a portion of a modified form of thermostaticswitch utilizing adjustable contacts.

My invention comprises an annular base pore tion I3 preferably formed ofsome relatively strong insulating material such as Bakelite or the like,to which is connected an arcuate metallic electrical conductive portionII. Screws or hollow rivets I2 (Figure 5) may be utilized for connectingthe arcuate conductive portion II to the insulating base ID.

A spacer block I3 (Figure 4) is connected to the insulating base ID bymeans of hollow rivets I4, and the rivets also connect a circularbimetallic strip I5 to the base portion.

The bi-metallic strip I5 is made up of a first lamination I6 of amaterial which has a high coefficient of thermal expansion and a secondlamination I! of a material having a lower coefficient of thermalexpansion. The two laminations are connected together substantiallythroughout their entire length as is common practice in bi-metallicstrips, and is bent around the insulating base portion Ill. Thebi-metallic strip l5 has two end portions I8 and I9, to which,respectively, there are connected two electrical contact members 20 and2 I. Except for the portion of the bi-metallic strip I5 which is inengagement with the spacer block I3, the entire strip and its contactmembers 20 and 2| are normally spaced away from the arcuate conductiveportion II and away from the base portion ID to allow for radialmovement of the bi-metallic strip I5, toward the circular base portionIll under the influence of a rising temperature until the contactmembers 20, 2| engage the arcuate conductive portion II. While this isthe preferred form of my invention it is to be understood that inanother arrangement, normally the contact members 20, 2| could be inengagement with the arcuate conductive portion II and be arranged tomove away therefrom under the influence of a rising temperature untilthe contact between the arcuate conductive portion II and the contactmembers 20, 2| is broken.

A first electrical lead 22 may be connected to the bimetallic strip I5by means of a screw 23 or the like, and a second electrical lead 24 maybe connected to the arcuate electrical conductive portion II. A hole 3|is provided in the bottom plate 26 through which the lead 24 passes, anda screw 32 connects the lead to the electrical conductive portion I I. Ascrew 33 is used to connect the lead 22 to the bi-metallic strip I5. Byutilizing screws 32, 33 for attaching the leads the switch may easily beput into an electrica circuit.

When the switch is closed the electrical circuit is from lead 22 throughthe bi-metallic strip I5 to the contact member 20 which is in contactwith the arcuate conductive portion I I and completing the circuitthrough the lead 24.

For ease in mounting the switch on walls or on timbers such as are foundin basements and for protecting the switch I provide a housing membercomprised of a top plate 25 and a bottom plate 26 of insulatingmaterial. The two plates 25 and 26 are held together and to the circularbase member H] by means of a hollow rivet 21 or the like which passesthrough the hollow center of the base member. Within the hollow centerof the base member If) I provide a centering washer 28 having a centralhole through which the hollow rivet 21 passes. One of the plates 25, 26may have an extended portion 29 through which there is a hole 30 bymeans of which the device may be easily mounted to some externalsupporting means such as a wall.

Figure 6 illustrates a modification of my device in which the arcuatemetallic electrical conductive portion H is adjustably mounted on thebase portion !0, and in which the contact members 20, 2| are adjustableto vary the temperature setting of the thermostatic switch. It is to beunderstood that either the conductive portion ll alone or the contactmembers 20, El alone, or both may be adjustable in a thermostaticswitch.

The conductive portion ll may be adjusted by means of the screws 35which extend through the conductive portion H and which have enlargedend portions 36. Screws 35 threadably engage the base portion to, andsprings 3'! are positioned around the screw between the base portion land the conductive portion H and tend to expand thereby biasing theconductive portion ll away from the base it. When the screws 35 areturned inwardly toward the base Hi the springs 3'1 thrust the conductiveportion ll toward the bimetallic member and as the screws 35 arewithdrawn from the base t) the springs 37 are squeezed and theconductive portion ll moves away from the bi-inetallic member :5.

Each contact member i=3 and El is adjusted by means of one of the twoscrews 38 to which it is connected. The screws 38 extend through thebi-metallic strip l and may be turned in one dir ction to advance thecontact members 20, 2i toward the conductive portion H, and turned inthe other direction to withdraw them away from the conductive portionII.

The temperature settin for a given thermostatic switch is set by thenormal spacing between the contact members 23, 2! and the conductiveportion ll. The closer the spacing between the contact members and theconductive portion the smaller the temperature change necessary to closethe switch.

My switch may be made either to open or close a circuit upon a rise intemperature, and it may be made to open or close a switch upon a drop intemperature.

One important use for my switch is to operate fire alarms, such as infactories and private homes, and may be made to operate from a lowvoltage source such as a door bell circuit. In such an installation itis desirable for the switch to normally be open and upon being heated toclose a circuit and ring a bell or otherwise operate an alarm device.

It is desirable that the switch operate in spite of a layer of dust anddirt which may gather on the contact members 2G, 2! and on theconductive portion H when the switch remains in an attic or basement fora long period of time, and it is desirable that the action of the switchbe rapid when it is heated.

By utilizing a circular construction as shown I obtain a sliding contactbetween the contact members 25, 2| and the conductive portion H whichbrealzs through any layer of dirt which may be present therebyestablishing a good contact, and by utilizing more than one contact iiimember I increase the chance for good contact under very adverseconditions.

In order to assure rapid action of the switch without resorting tosnap-action types which are more expensive and which may becomeinoperative due to dirt, I position the bi-metallic strip l5 around thebase ill with the portion l6 which has the higher coeiiicient of thermalexpansion on the outside where it more readily receives the heat, andwith the portion ll which has the lower coeilicient of thermal expansionon the inside where it is shielded on one side by the portion I! and onthe other side by the central base portion i i. Thus, even the slightestamount of heat is utilized to cause a bending of the bimetallic stripi5, and if the amount of bending is sufficient the switch will beclosed.

While I have described my invention with a certain degree ofparticularity it is to be understood that numerous changes in theconstruction and the arrangements of the parts may be made withoutdeparting from the spirit and scope of my invention.

I claim as my invention:

1. In a thermostatic switch, a circular base portion, an arcuateelectrical conductive portion connected to said base at one sidethereof, an arcuate oi-metallic electrical conductive portion connectedto said. base at the opposite side thereof, said bi-metallic portionbeing wrapped about base and having two contact portions each of whichis positioned in over-lapping relation with a portion of said arcuateelectrical conductive portion and each of which is adapted to engage theconductive portion to make an electrical circuit, only two electricalterminal means one of which is electrically connected to said arcuateelectrical conductive portion and the other of which is electricallyconnected to said lei-metallic portion, a top cover and a bottom covereach connected to said base portion and extending outwardly from saidcircular base around the periphery thereof, said bi-metallic portionbeing protected on three sides by said base and said two covers, andsaid lei-metallic portion having its portion with a higher coefficientof thermal expansion positioned to the outside of the portion with thelower coefiicient of thermal expansion whereby the portion with thelower coefficient is protected on four sides.

2. In a thermostatic switch, a cylindrical base portion, an arcuateelectrical conductive portion connected to said cylindrical base at oneside of its outer face, an arcuate bi-metallic electrical conductiveportion connected to said cylindrical base at the opposite outer facethereof, said bimetallic portion being wrapped about said cylindricalbase and having two contact portions each of which is positioned inover-lapping relation with a portion of said arcuate electricalconductive portion, only two electrical terminals one of which iselectrically connected to said arcuate electrical conductive portion andthe other of which is electrically connected to said bi-metallicportion, either of said two contacts of said bimetallic portion uponengaging said conductive portion establishing an electrical circuitbetween said two terminals.

3. A thermostatic switch comprising, in c0n:bination, a base, anelectrical conductor connected to said base, a bi-metal connected tosaid base and having two contact portions each positioned in overlappingrelationship with a portion of said electrical conductor, said bi-metalbeing in substantially an arc of a first circle and aid elec tor and theother connected to said bi-metal, said 10 bi-metal being arranged sothat upon a change in temperature in one direction each of said twocontact portions moves with respect to said electrical conductor to makea single electrical circuit upon either one of said two contact portionsen- 15 1,832,761

gaging said electrical conductor and upon a change in temperature in theopposite direction to break the circuit upon both of said contactportions disengaging from said electrical conductor.

HERBERT E. WHITE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 352,442 Bulen Nov. 9, 1886978,983 Brent Dec. 20, 1910 Brady Nov. 17, 1931

